A check valve may be mounted on a fuel tank of an automobile or the like to prevent a fuel tank from bursting or the like by discharging fuel vapor to an outside when the pressure within the fuel tank rises to a positive-pressure threshold or higher, while it also prevents the fuel tank from being crushed or the like by taking outside air flow into the fuel tank from the outside thereof when the pressure within the fuel tank drops to a negative-pressure threshold lower than the atmospheric pressure.
JP-UM-S62-037677-A discloses from the third page, line 11 to the fourth page, line 6, and FIG. 2, a check valve assembly including a cup-shaped tubular body including a connection port connected to its one end on a tank side, and a connection port connected to the other end on a canister side, an operation cylinder having the H-like cross section, which is disposed slidably inside of the tubular body, a partition wall with a hole, which is disposed in the middle in the shaft direction of the operation cylinder, an umbrella valve (mushroom valve) made of rubber that is mounted on the partition wall and arranged to close the hole in a normal state, a cylindrical frame arranged to fit into the other opening of the operation cylinder, a cylindrical valve made of rubber mounted on the cylindrical frame, and a coil spring arranged to urge the operation cylinder toward the connection port on the canister side.
In the normal state of the check valve assembly, the operation cylinder is urged by the coil spring and the cylindrical valve closes the connection port on the canister side. When the tank internal pressure rises, however, the umbrella valve is pressed and deformed so as to open the hole in the partition wall and discharge the fuel vapor or the like to the canister side. On the other hand when the tank internal pressure drops, the operation cylinder is pressed against the urging force of the coil spring so that the cylindrical valve opens the connection port on the canister side to take the outside air flow into the tank.
However, in JP-UM-S62-037677-A, the umbrella valve needs to be mounted by inserting a shaft portion thereof into a mounting hole in the center of the partition wall of the operation cylinder that slides in the cup-shaped tubular body. On top of this, the cylindrical valve needs to be mounted by inserting a shaft portion thereof into the mounting hole of the cylindrical frame that is fitted into the other end of the operation cylinder. These assembling works are complicated and cumbersome, which arises problems in assembly workability.